1. Field of the Invention
The present invention relates to electric power tools. More particularly, the present invention relates to a structure for attaching brush holders for holding brushes, such as carbon brushes, in predetermined positions of a housing and against a commutator motor of an electric power tool.
2. Description of the Related Art
In some electric power tools and other motor-driven appliances and devices to which the present invention is applicable, brush holders are attached to the housing with rivets or calking pieces provided on the brush holders so as to hold the brushes against the commutator of the motor of the tool. In another structure for attaching brush holders, brush holders are provided with barbed lugs for fitting into through-holes in the housing.
Such conventional structures, however, suffer from various shortcomings. Attachment of brush holders with rivets and calking pieces is time-consuming and thus reduces the efficiency at assembly sites. Moreover, as rivets must be provided as separate parts, they also raise the manufacturing cost of the entire devices. Although structures using barbed lugs require no separate parts, lugs often need to be fitted into the through-holes with jigs due to the difficulty in maintain close manufacturing tolerances.
Furthermore, brush holders are sometimes removed from electric power tools in order to recycle the housings. Such removal is troublesome if barbed lugs, rivets, or calking pieces are employed to secure the brush holders to the housing.
Various improved structures have been proposed to overcome the aforementioned shortcomings. For example, Japan Published Unexamined Utility Model Application No. 50-72901 discloses such a structure in which each of the two brush holders is set in a recess formed in a first housing portion and provisionally held in the recess with a L-shaped elastic member. According to this structure, the brush holders are secured by fitting a second housing portion to the first housing portion. Japan Published Unexamined Utility Model Application No. 7-27274 discloses another example, in which a pair of brush holders is received in a pair of grooves in a first housing portion, and a pair of ribs formed on the inner surface of a second housing portion is brought into contact with and secures the brush holders when the second housing portion is assembled to the housing portion. The first structure, however, still requires additional parts (the elastic members) in order to provisionally retain the brush holders in the recesses, whereas the brush holders of the second structure are not stably seated in the grooves or accurately positioned during the assembly thereof, thus affecting mounting or replacement of the brushes and connection and wiring of leads to the holders.